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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"casting pointers to/from char * switches endianity","articleBody":"This is most likely a gdb bug, we IIRC we agreed to collect all issues here.\r\nWith the not-yet-commited ppc64 arch support from Jeff, on 11SP4 ppc64 kernel dump (thus big endian), with crash-python running on x86_64, I see the following problem:\r\n\r\n\u003e\u003e\u003e print(gdb.Value(0xc0000007ef86f5f0).cast(gdb.lookup_type('struct list_head').pointer()))\r\n0xc0000007ef86f5f0\r\n\r\nOK so far\r\n\r\n\u003e\u003e\u003e print(gdb.Value(0xc0000007ef86f5f0).cast(gdb.lookup_type('char').pointer()))\r\n0xc0000007ef86f5f0 \"\\300\"\r\n\r\nalso OK, but:\r\n\r\n\u003e\u003e\u003e print(gdb.Value(0xc0000007ef86f5f0).cast(gdb.lookup_type('struct list_head').pointer()).cast(gdb.lookup_type('char').pointer()))\r\n0xf0f586ef070000c0 \u003cerror: Cannot access memory at address 0xf0f586ef070000c0\u003e\r\n\r\nI.e. casting from one kind of pointer to char pointer switches endianity.\r\n\r\nOpposite direction as well:\r\n\r\n\u003e\u003e\u003e print(gdb.Value(0xc0000007ef86f5f0).cast(gdb.lookup_type('char').pointer()).cast(gdb.lookup_type('struct list_head').pointer()))\r\n0xf0f586ef070000c0\r\n\r\nInterestingly enough, when \"char *\" is not involved at all...\r\n\r\n\u003e\u003e\u003e print(gdb.Value(0xc0000007ef86f5f0).cast(gdb.lookup_type('struct page').pointer()).cast(gdb.lookup_type('struct list_head').pointer()))\r\n0xc0000007ef86f5f0\r\n\r\nThis breaks the current implementation of container_of(), I have modified it locally to cast to long instead of charp.","author":{"url":"https://github.com/tehcaster","@type":"Person","name":"tehcaster"},"datePublished":"2019-02-07T08:05:11.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/29/crash-python/issues/29"}